Intra-specific variability can be used as an important tool to contrast and mitigate the negative impacts of climate change. In particular, under Mediterranean climate conditions, drought stress is becoming a crucial issue for growers. Vine performance, taking into account vine yield and grape composition, is dependent on the vine capability of assimilating CO2 and fix it into carbohydrates throughout the whole season. Under water stress, stomatal regulation, that allow plants to prevent excessive water loss and tissue drying, limits leaf gas exchanges. Understanding the mechanisms regulating stomatal closure is crucial to determine the behaviour of genotypes under water stress. Two main mechanisms are accredited for controlling stomatal conductance under water stress: active mechanisms, based on the biosynthesis of hormonal signals, mainly abscisic acid (ABA), and passive mechanisms, mainly based on the variation of leaf turgor pressure as the plant water potential decreases during water stress. New research evidences pointed out that the capability of genotypes to close stomata at a given stem water potential threshold was correlated with its xylem vulnerability to cavitation. ABA accumulation in the leaf appears to be subsequent to stomata closure suggesting that, in vivo, stomatal conductance mainly rely to passive mechanism rather than to active ones. Hydraulic properties of each genotype appear to control their stomatal behavior under water stress consistently with the rising opinion that intraspecific variability of stomatal behavior cannot be discriminated into two different categories (isohydric and anisohydric) but should be represented as a continuum of genotypes with different levels of anisohydry. These results underline the need to learn more about the phenotype of grape cultivars. Growers will be able to use such information by planting more tolerant genotypes depending on the vineyard condition and to use different water potential thresholds for irrigation scheduling.
Keywords: water stress, Vitis vinifera, abscisic acid, water potential, gas exchange